In the race for who shall fill the last four years of the Senate term of the late Hubert H. Humphrey, Rep. Donald M. Fraser (D-Minn.) yesterday claimed that poll results showed him with an almost 2-to-1 popularity lead over appointed Sen. Muriel Humphrey among Democrats elected state party convention delegates at recent neighborhood caucuses.

The caucuses, which were held Tuesday night, are the first step in a series of regional conventions for Minnesota political parties that lead to state conventions in June where a candidate must attract 60 percent of the delegate votes to be endorsed.

Fraser based his claim of a 40 percent to 23.3 percent lead over Humphrey on a sampling of 902 delegates elected at 150 of the 4,000 precinct caucuses Tuesday night. He also said the "systematic" poll found 15.9 percent still undecided. Rick Scott, state party chairman, said a sampling at the cauccuses by the state Democratic headquarters found far more undecided.

"I am encouraged by the show of strength for my candidacy for the U.S. Senate," Fraser said in a statement from his Minneapolis campaign office. But Humphrey, in a statement released by her senatorial office, said in effect it was too early to tell how the selection of any nominee will shape up.

Unlike Fraser, who has been campaigning hard, Humphrey hasn't announced whether she will seek endorsement for election. She was appointed to succeed her late husband, who died of cancer in January, until the November general election, and despite heavy pressure from many quarters to run, she has delayed a decision.

Supporters of Humphrey, who assume she would be virtually unbeatable if she runs, were surprised by Fraser's apparently commanding frontrunner position. But precinct spot checks found that some of his strength seems to hinge on Humphrey not running.

In other precincts Fraser won mild support although most delegates took a wait-and-see attitude, according to Democratic Chairman Scott. He said his survey showed most delegates elected to the next level of conventions were uncommitted, although he conceded Fraser and Humphrey were the leading candidates.

In his own poll, Fraser ran far ahead of Nicholas Coleman, Minnesota Senate majority leader, and Rep. James Oberstar (D-Minn.), who announced on the eve of the caucuses that he wasn't a candidate and urged Humphrey to run. He said the Humphrey name at the top of the ticket would be worth 100,000 votes --"Muriel can just smile her benign benevolent smile and she will help Wendel Anderson win." That was an allusion to incumbent Sen. Anderson (D-Minn.), who is running for a full term after having arranged his own appointment to the Senate.

On the Republican side, a 66-precinct sample by the Republican State Central Committee showed Rep. Al Quie (R-Minn.), a candidate for the governorship held by Democrat Rudy Perpich with an 80 percent majority over his nearest competitor, David Duremberger.

Scott said there was a record turnout in rural areas, and 40 percent of the caucuses passed resolutions asking for government action to raise farm prices.

The Republican state headquarters said a majority of their precinct caucuses took an antiabortion position, but for the Democrats, according to party leaders, the issue was not as hot as they had feared. Apparently about half of the caucuses debated it.